Telephone system



Oct. 4, 19380 H. HOVLAND TELEPHONE SYSTEM Filed Jane 11, 1935 3Sheets-Sheet 1 ATTORNEY Get. 4, 3938. H. HOVLAND TELEPHONE SYSTEM FiledJune 11, 1935 3 Sheets-Sheet 2 @NN WNW l/vl/ENTOR H HUI LAND 77ORNEi H.HOVLAND TELEPHONE SYS TEAM Filed June 11, 1955 5 Sheets-Sheet 3m/vavro/v H. HOVLA/VD ATTORNEY Q nut Patented Oct. 4, 1938 PATENTOFFlCE.

TELEPHONE SYSTEM Henry Hovland, Williston Park, N. Y., assignor to BellTelephone Laboratories, incorporated, New York, N. Y., a corporation ofNew York Application June 11,

9 Claims.

This invention relates to telephone systems and particularly toautomatic systems having coin controlled lines.

The objects of the invention are to improve a the dialing operation; toguard against fraudulent operation of the pay station; to reduce thenumber of current changes in the line; and to effect other improvementsin systems of this character.

It has been proposed heretofore in party line systems, where a groundconnection at one of the substations serves as a means for identifyingthe station when calling, to remove such ground connection duringdialing in order to improve the pulsing conditions at the centraloflice.

It is also well known to perform certain tests on coin lines todetermine the presence or absence of a coin at the pay station, and insome cases circuits have been devised todetect fraudulent manipulationby the party at the coin sta tion.

According to a feature of the present invention, the ground connectionthat is applied when the coin is deposited to initiate the call and tomake it possible for the patron to dial, which ground connection isnecessary subsequently for the disposition of the coin, is automaticallyremoved from the line while the dial is sending impulses toset theswitches in the central office. This makes it possible to improve theoperation of the impulse mechanism that responds to the substation dialand also to avoid the use of impulse repeating equipment at the centraloffice. Moreover, the elimination of this repeating equipment simplifiesthe operation of the central oflice circuits, particularly on calls toan operator. Heretofore, on calls to the operator it has been thepractice to remove the repeater, following dialing, by a currentreversal the same as on full dial calls to subscribers. But this,reversal also sets the circuits to collect the coin, whereas oftentimesthe calls to operators require no charge, thus making it necessary forthe operator to refund the coin. With the present invention there is norepeater to be removed, and the circuits can be arranged to refund thecoin in all cases on calls to the operator unless she disposes of itbefore release.

' Another feature is a system in which a test of the line is made whencollect current is applied to determine if a ground connection ispresent at the substation. If not, an alarm is given. If, however, thefirst test shows a ground present, a second test is made to determine ifthe ground 1935, Serial No. 26,014

was removed by the collect or refund current or if it continues to existfollowing the removal of such current. If it does continue, thisindicates either that it is a fraudulent ground or that the patron hasdeposited another coin immediately following the disposition of thefirst coin and wishes to make a second call. Accordingly, a third testis then made to determine whether the ground is fraudulent or is theresult of a newly deposited coin. In case this latter test finds theground was fraudulently applied, an alarm is given. But, if it finds asecond coin has been deposited, the original connection of the line tothe selector is held, and the patron is free to proceed with the dialingof the new connection.

A further feature is an improved release arrangement whereby it ispossible to release the established connection although the coin groundis maintained on the line following the replacement of the receiver atthe pay station. Since the coin ground remains on one side of the line,tip side, after the receiver is replaced, and since the line relay inthe final switch has its battery winding connected to the other side,ring side, of the connection, which is reversed when the calledsubscriber answers, this relay will continue to hold in a circuit to thecoin ground. To enable release under this condition, a control relay isinserted in the ring side of the trunk preceding the first selector.This relay releases when the calling party hangs up his receiver, and itopens the circuit of the line relay causing the release of allselectors. In this way it is unnecessary to introduce, as is sometimesdone, a second reversal of the talking conductors to neutralize theeffect of the reversal caused by the answer of the called subscriber.Not only is the system simplified by the elimination of a currentreversal but the consequent changes of current in the telephone receiverat the calling station are also obviated.

The foregoing and other features of the invention will be described morefully in detail in the following specification.

Fig. l of the drawings shows a coin-box station and line arrangedaccording to this invention and connected at a stepby-step centraloffice to a line circuit of the Well-known type to which the usual linefinder, shown schematically, has aca cess.

Fig. 2 which connects with Fig. 1, shows the circuit details of acoin-box trunk circuit arranged according to this invention and connect-.ing with Fig. 3 through a first and second selector of the usualstep-by-step type, indicated here in an abbreviated schematic form.

Fig. 3 shows circuit details of a well-known arrangement of astep-by-step connector circuit, the brushes of which have access to theterminals of a subscribers line, and also of a trunk circuit extendingto an operators position.

The system will now be described in detail. Let it be assumed that thesubscriber of station IOI desires to establish a connection with thestation 33L When a coin I03 is deposited and receiver I02 is removedfrom the associated switchhook, a circuit is closed for operating linerelay I05. This circuit may be traced from central oflice batterythrough the winding of relay I05, left-hand contacts of cut-off relayI06, over lower conductor of line I04, through lower contacts of dialI07, transmitter I08, switchhook contacts I09, upper normally closedcontacts of dial I 01, winding of coin magnet H and coin operatedcontacts II I to ground. Coin magnet H0 is marginal and does not operatethrough this circuit. Line relay I05, in operating, connects batterythrough its right-hand contacts and the winding of cut-off relay I06 andresistance I I 2 in multiple to the sleeve terminal of line finder LFand also connects ground with its left-hand contacts to a relay, notshown, in the circuit of line finder LF, which causes it to hunt forthis line. When terminals H3 are seized and the connection is extendedover conductors II 4 to Fig. 2, ground is-connected to the sleeveterminal, operating relay I06 through the righthand operated contacts ofrelay I05. vRelay I06 locks to the sleeve terminal and opens the circuitthrough the winding of relay I which releases.

When the coin-box trunk of Fig. 2 is connected to the line I04,ashereinbefore described, a circuit is closed for operating relay 20Iwhich may be traced from battery through the winding of relay 20I, lowernormally closed contacts of relay 202, lower normally closed contacts ofrelay 203, lower inner contacts of relay 204, lower normally closedcontacts of relay 205 thence over the ring conductor and through thering contacts of line finder LF, over the lower conductor of subscriberline I64 through lower normally closed contacts of dial I01, transmitterI08, switchhook contacts I09, upper normally closed contacts of dialI01, winding of coin magnet H0 and coin operated contacts I I I toground. From switchhook contacts I09 another circuit to ground may befollowed through the right-hand winding of induction coil H5, over theupper conductor of line I04, through upper contacts of line finder LF,upper inner back contacts of relay 205, upper winding of polarized relay206, upper contacts of relay 20'! and to ground through one winding ofthe line relay, not shown, of first selector SI. Relay 206 is poled sothat it does not operate at this time. Relay MI, in operating, operatesrelay 204 from battery through the upper winding of relay 204, upperouter contacts of relay 20I, upper outer normally closed contacts ofrelay 205 to ground on the upper inner break contacts of relay 203.

The operation of relay 204 opens the operating circuit of relay 20Ipreviously traced. Relay 20I releases, opening the operating circuit ofrelay 20 but relay 204 does not release as its upper contacts closebefore its other contacts function, thereby assuring the locking ofrelay 204 to sleeve conductor 208 to which ground was connected when theline relay of selector SI operated. Relay 204 also operates with itslower outer front contacts relay 203 which, in operating, opens thedirect current path between sleeve conductors 208 and 209 and connectsconductor 209 to ground through the winding of retardation coil ZIQ,thereby preventing the immediate releaseof line finder LF when ground isremoved from conductor 208 after the disconnection of station i0I. Thisdelay in the release of the line finder LP is to hold the connectionuntil the coin relay H0 has operated. This feature will be describedsubsequently. The calling subscriber of station IOI may now dial thenumber of the called station 30L When the dial I0! is moved off-normal,the upper break contacts open, disconnecting the ground through coinrelay H0 and providing thereby a clear metallic circuit for pulsing. Ashereinbefore stated this feature of the invention improves the pulsingcircuit, making it unnecessary to use impulse repeating equipment at thecentral ofiice, as heretofore, to provide forv the loss of pulsing rangedue to the coin-box ground. Pulses from dial I07 are transmitted by thelower of pulsing contacts of dial I01, through its operated off-normalcontacts, and the right-hand Winding of induction coil I I5 over the tipand ring conductors of Figs. 1 and 2, the connection being extended inthe usual manner through selectors SI and S2. The pulsing current passesthrough the windings of polarized relay 206, but this relay does notoperate at this time as the direction of current opposes operation. Thepulsing current is also without effect on relay 2 I I as the winding ofthis relay is short-circuited through break contacts on relays 2I2 andM3. When brushes 2 I4 of selector S2 connect with the terminals of theconnector of Fig. 3, the pulsing circuit is extended through upper andlower outer break contacts of reversing relay 303 to the winding ofrelay 302 which operates over the subscribers loop.

The calling subscriber now dials the tens digits of the called number.When relay 302 operated it operated, through an obvious circuit, relay304, which connects ground to sleeve lead 305,- therebyholding operated,in the usual manner the preceding switches and guarding the connector ofFig. 3 from seizure by other selectors. On the first break of the dial,relay 302 releases and closes a circuit from ground on its back contactsthrough the operated upper front contacts of relay 304, normally closedcontacts of vertical off-normal springs VON and windings of relay 306and vertical magnet 30? to battery. Relay 306 and vertical magnet 36'!operate. Relays 364 and 306 are slow-to-release and do not re leasebetween breaks of the dial. As soon as the shaft moves one vertical stepthe VON springs operate and the energizing circuit for relay 306 andmagnet 30? is transferred from conductor 308 to conductor 309, and iscompleted through the operated front contacts of relay 306. Verticalstepping continues until the level is reached in which are located theterminals of the called line.

Afterthe pulsing of the tens digit isrthus completed, relays 302 and 304both being operated, the circuit through the winding of relay 306 andmagnet 30'! is opened. Relay 306 releases and transfers the pulsing lead309 to lead 3I0 to provide for rotary stepping.

On the first break of the dial for rotary stepping, that is, for dialingthe units digit of the called number, ground on conductor 3) operatesrelay 3| I through the lower outer break contacts of relay 312, and inmultiple with relay 31 1, operates rotary magnet 313 through the lowerouter break contacts of relay 310. When relay 311 operates, it looks toconductor 310 and being slow to release remains operated during thedialing of the units digit. lf'he operation of rotary magnet 313 causesthe shaft to step in a rotary direction until the terminals of thecalled line are seized by the brushes 3&3. After the last pulse isdelivered and relays 302 and 3114 are both operated, the circuit throughrelay 311 and magnet 313 is opened. Before slow releasing relay 311releases, however, if ground is found on the sleeve of the called lineindicating that it is busy, relay 312 operates from battery through itswinding, upper inner break contacts of relay 3M, lower operated makecontacts of relay 31 1 to the aforesaid busy ground. When. relay 311finally releases, a circuit is closed for locking relay 352 which istraced from battery through the winding of relay 312, upper inner breakcontacts of relay 314, lower'inner break contacts of relay 3! 1, andlower inner operated make contacts of relay 312 to ground on conductor365. Relay 3i2 operated connects a busy tone potential from transformer315, through an interrupter not shown, to the ring conductor through itsupper make contacts.

The calling subscriber of station ill! on hearing the busy tone will nowhang up the receiver, opening the circuit over the loop causing therelease of relays 392 and 3%. Relay 3% in releasing removes ground fromthe release lead 395, causing the release of selectors S1 and S2 and ofrelay 312. A circuit is also closed for the operation of the releasemagnet 3? which is traceable from battery through the winding of magnet316, upper operated make contacts of springs VON, upper outer breakcontacts of relay 3, and break contacts of relays tilt and 302 toground. Release magnet 319 now restores the connector switch, includingsprings VON, to normal. When ground is removed from the sleeve lead 298by the release of the selectors, relay 2134 releases, which operatesrelay ilfilthrough a circuit from battery; through the winding of relay2d 1, normally closed contacts of relay 202, lower operated inner frontcontacts of relay 293 to ground on the lower outer back contacts ofrelay 204. The release of relay 2M also opens the holding circuit forrelay 293 which is slow to release and remains operated until relay 215operates as hereinafter described. When relay 291 operates, it closes acircuit for operating relay 295 which is traced from battery through thewinding of relay 235, lower outer make contacts of relays 201 and 2%,lower inner front contacts of relay 2% to ground on the lower outer backcontacts of relay sea. When relay Edi operates, it connects negative orreturn coin bat- .te'ry MB to the tip and ring conductors leading to thecoin-box station M1. This connection is made from battery 216,resistance lamp 2 ll, lower outer back contacts of relay 2E3, winding ofrelay 215, upper and lower operated inner make contacts of relays 291and 295, thence over the tip and ring conductors to station 1E1, wherenegative potential from the aforesaid battery 2th is applied from thetip conductor through righthand winding of induction coil H5, uppernormally. closed contacts of dial ml, to the winding of coin magnet 110,grounded through the coin operated contacts 1 1 i. As the receiver atstation 191 is on its switchhook, the negative coin battery over thering conductor is inefi'ective at this time due to switchhook contact139 being open. Coin magnet 1111 which is polarized is, however,

energized over the tip conductor and actuates its armature in thedirection to cause the return of the deposited coin 103. Relay 215operates through the circuit above traced and closes a holding circuitfor relay 2113 which may be followed from battery through the winding ofrelay 2B3, lower middle break contacts of relay 21M,

292 is slow to operate so as to delay the release of relay 291 until thecoin relay 110 has completely operated. When relay 201 releases thecircuit through coin relay H6 and relay 215 is opened. Relay 215releases and springs H1 of the coin magnet 1 15' are opened, removingground from the tip of the line. The release of relay 215 allows relays2G2, 2E3 and 295 to release. The release of relay 295 allows the linefinder LP and cut-off relay 1136 to release, all apparatus now beingrestored to normal.

The operation has been described for the condition existing when theline of the called station is busy. If the subscriber of the callingstation should abandon the call, that is, hang up the receiver at anytime before the terminals of the called'line have been seized by thebrushes 383 of the connector of Fig. 3, the system functions in asimilar manner to cause the refund of the tie posited coin 103. Afterselectors S1 and S2 release, ground is removed from sleeve lead 2538,causing the release of relay 2134. The sequence of relay operations thatfollow thereafter are the same as those hereinbefore described. Theoperation of the system will now be discussed for the condition whereinthe call to the called line is completed.

For a completed call, the discussion will be continued from that pointof the hereinbefore given description at which the connector brushes 303seized the terminals of the called line and found them busy. Let it beassumed that the line is not busy and that battery is found on thesleeve terminal. Relay 3M operates from ground on the lower outeroperated contacts of relay 304 through lower inner break contacts ofrelay 312, upper winding of relay 314, lower outer break contacts ofrelay 311 to battery on the sleeve brush 303 and seized sleeve terminalof the called line. Relay 31 1, in operating, looks through its lowerwinding and lower inner make contacts to ground on the lower inner makecontacts of relay 3M and grounds through its upper inner make contactsthe sleeve of the called line, thereby guarding the line against seizureby another connector. The operation of relay 314 also connects, with itsupper outer make contacts, conductor 31'! through to the tip terminal ofthe called line, and with its lower outer make contacts connectstheconductor 318 through to the ring terminal of the called line.

Ringing current is not connected to the called line until relay 319operates from ground 321] supplied through a pick-up interrupter circuitwhich is of the usual well-known arrangement and is not shown here indetail. Relay 319 operates from ground 32D, operated contacts 342 ofrelay 314, lower break contacts of relay 319, upper inner break contactsof relay 322 to battery through the winding of relay 319. Relay 319looks to ground on conductor 305. When relay 319 operates, ringingcurrent is supplied from source 321 through an interrupter circuit, notshown, upper operated front contacts of relay 319, upper winding ofrelay 322, lower outer back contacts of relay 322, over conductor 318,through lower outer make contacts of relay 314, ring brush 303 andassociated contacts, thence over the conductors and through the station301 of the called subscriber's line, through tip brush 303 andassociated contacts, upper outer make contactsof relay 314 and upperouter break contacts of relay 322 to ringing ground 323. Relay 322 isslow to operate and does not operate on ringing current through theringer, not shown, at station 301.

When, however, in response to the sound of Y the ringer the subscriberof station 301 answers, a bridge of low impedance is connected acrossthe line at station 301, which now causes relay 322 to operate, closingfirst its lower middle make contacts and thereby through its lowerWinding a locking circuit to ground on the lower inner make contacts ofrelay 304. The operation of relay 322 through its lower winding opensthe initial operating circuits through its upper winding, therebydisconnecting ringing current from the line of station 301 and connectsconductors 311 and 318 through its upper and lower outer contacts totalking conductors 324 and 32 5, respectively, completing thereby thetalking connection. If the called subscriber answers during the silentperiod, then relay 322 operates from battery on the upper back contactsof relay 319. When relay 322 operates, it releases relay 319 if thisrelay has previously operated. Relay 303 now operates from battery andground through its upper and lower windings, over conductors 324 and 325and thence through operated contacts of relays 322 and 314 and the loopof station 301. In operating, relay 303 reverses the current from relay302 that is transmitted back to the station 101 of the calledsubscriber, causing the operation of polarized relay 208. When relay 206operates, the operation of charge relay 213 is delayed for a minimumperiod of about two seconds so as to avoid the possibility of chargingon a momentary operation of relay 206. This is accomplished by the useof the pick-up relay 212 which operates from battery through itswinding, operated contacts of relay 206, lower break contacts of relay212, lower inner break contacts of relay 213 to ground on interrupterdrum 224. Relay 2 12 looks to ground through itslowerinnermake contactsand contacts 225 of relay 213, and closes an obvious circuit through theright-hand winding of start relay 226 which operates and connects withits right-hand contacts battery to motor 221 which starts and causes therotation of interrupters 222, 223 and 224. When drum 223 rotates through180 degrees, lead 221 is grounded causing the operation of relay 213through lower break contacts of relay 201 and upper inner operatedcontacts of relay 212. Relay 213 looks through its upper inner contactsto ground on lead 209, through the upper outer contacts of relay 220 andopens the circuit of relay 212 which releases. When drum 222 has rotatedthrough 360 degrees, the locking circuit through the left-hand windingof. relay 226 is opened, relay 226 releasing and opening the circuitthrough motor 221. Interrupter drums 222, 223 and 224 are accordinglyagain in their normal positions as shown by the drawings. When relay 213operates, it also opens with its upper inner break contacts the shortcircuit around the winding of relay 211 which operates on the currentover the calling subscribers loop thereby avoiding the operation ofrelay 201.

When the subscriber of station 101 hangs up his receiver, the line loopis opened by switchhook contacts 109 and the ground through the coinrelay winding remains on the top side of the line. If the called station301 has not hung up, the coin ground over the tip side of the line willhold operated relays 302 and 304 and thereby hold the connection.However, relay 211 releases and connects ground to the winding of relay201 through the upper outer make contacts of relay 213. Relay 201operates and opens the tip side of the line and allows selectors S1 andS2 to release. Relay 201 is arranged to operate slowly to avoidreleasing the circuit on a momentary opening of the line loop such asmay occur if the dial is operated inadvertently. The release of theselectors S1 and S2 removes ground from the sleeve conductor 208 whichallows relay 204 to release. Relay 203 is'now held from battery throughits winding, lower middle break contacts of relay 204, operated contacts228 of relay 213, break contacts of relay 202, over conductor 2| 9,through lower inner make contacts of relay 203 to ground on the lowerouter break contacts of relay 204. The release of relay 204 operatesrelay 201 from battery through the winding of relay 201, break contactsof relay 202, to ground on conductor 219. Relay 201 operates relay 205from battery through its winding, lower outer make contacts of relay201, lower outer make contacts of relay 203 to ground on conductor 219.Positive coin battery 229 is connected through resistance lamp 230,lower outer front contacts of relay 213, winding of relay 215, upper andlower inner front contacts of relays 201 and 205 to the tip and ring ofthe line to the calling station. Under normal operating conditions,ground is at this time connected to the winding of coin relay 110 due tothe operation of the contacts 11 1 by the coin 103. Relay 215 operatesin series with the winding of coin relay 110 which operates and collectscoin 103. Relay 215 closes an obvious circuit through the winding ofrelay 202. Relay 202 is slow to operate and after an intervalsufliciently long to assure the operation of coin magnet 110, relay 202operates and releases relay 201, disconnecting positive coin battery 229and releasing relay 215. Relay 215 releases slowly and after an intervalsufficient to assure the release of coin relay 110 closes a circuit foroperating relay 220 over the tip of the line. This circuit is tracedfrom battery, through the winding of relay 220, upper inner backcontacts of relay 220, lower outer make contacts of relay 213, upperbreak contacts of relay 215, upper back contacts of relay 205 to the tipconductor, relay 205 being held through lower outer.

make contacts of relay 202 to ground on conductor 219. Under normalconditions, coin 103 having been collected and contacts 103 being open,there will be no ground at station 101. Consequently, relay 220 does notoperate and does not close with its lower make contacts locking circuitsfor relays 202 and 203, which accordingly release after an intervalsince relay 203 is slow-to-release and likewise relay 202 under controlof relay 203. Relay 202 in releasing releases relay 205 which, inreleasing, releases the line finder LF and also relay 213. All apparatusis now restored to normal.

From the hereinbefore given description, it is seen that the purpose ofrelay 220 is to test for ground at the calling station, immediatelyafter the application of positive coin battery potential. If the groundat the calling station is due to the deposit of a second coin then relay220operates through the winding of coin magnet I I0 to ground over thetip conductor. The locking contacts of relay 220 close first before theinitial operating circuit through the upper inner back contacts isopened and relay 220 looks to ground on conductor 2I9. Relay 220, inoperating, closes a circuit for maintaining relay 203 operated. Thiscircuit extends from battery through the winding of relay 203, lowermiddle break contacts of relay 204, lower middle make contacts of relay220, lower inner make contacts of relay 203 to ground on the lower Outerbreak contacts of relay 204. Relay 220 also closes another circuit formaintainingrelay 205 operated. This extends from battery through thewinding of relay 205, lower outer make contacts of relay 220, to groundon conductor 2 I 9. Relay 202 is also held through its lower inner makecontacts to ground on conductor 2I9. Relay 2 20 closes a circuit foroperating relay 204 which may be traced from ground through lowerwinding of relay 204, upper inner make contacts of relay 220, lowerouter make contacts of relay 2I3, upper break contacts of relay 2I5,upper break contacts of relay 20I, upper inner operated from contacts ofrelay 205 thence over the subscribers loop, through lower inner operatedmake contacts of relay 205, upper outer make contacts of relay 220 tobattery through resistance 23!. Relay 2I3 is slow to release on theopening of its locking circuit by the opening of the upper outer breakcontacts of relay 220 so that relay 204 can operate before its operatingcircuit is opened by the release of relay 2I3. Relay 204 looks to groundon conductor 208 through its upper winding and removes ground fromconductor 2I9, thereby releasing relays 202, 205 and 220. From thispoint, the second connection is established as described for theoriginal call.

Let it be assumed now that an attempt is made at station IOI to obtain aconnection fraudulently by connecting a direct ground to the tip of theline, instead of making the ground connection in the legitimate mannerby the insertion of the coin I03. In this case, the system functions ashereinbefore described except that now relay 204 does not operate afterrelay 220 has operated due to the fraudulent ground connected to the tipconductor at station IOI. This follows from the fact that this groundacts as a low resistance shunt on the lower winding of relay 204,preventing its operation as hereinbefore described. When relay 204 failsto operate, ground is maintained on conductor 2I9, thereby preventingthe release of relays 202, 203, 205, and 220. The operation of relay 220releases relay 2I3, and when this relay releases, the operating circuitthrough the lower winding of relay 204, hereinbefore traced, is opened,so that if the fraudulent ground at station ml is subsequently removedand a coin is deposited, relay 204 will not operate. Accordingly, withthe locked-up condition just described existing, ground on the upperouter contacts of relay 205, after a predetermined interval, causes analarm circuit, not shown, to function and thereby to indicate to themaintenance force at the central oflice, that the apparatus at stationIOI has been manipulated in an irregular manner.

The system has been discussed for fraudulent operation at the callingstation, when a direct ground was applied to the tip conductor of theline and maintained during the established connection. The system alsofunctions so as to give an alarm, if the ground is applied to the tipconductor only momentarily-0nly sufiiciently long to cause the operationof the line finder and connection to a selector. When, after thereceiver at the calling station has been restored to the switch-hook,the positive coin battery 229 is connected to the tip and ringconductors through the winding of relay 2 i 5 and there is no groundexisting at station IOI, relay 2 I5 does not operate, and consequentlythere can be no further operation as described hereinbefore. Relay 205remains operated and after an interval effects the sounding of the alarmby the ground on its upper outer contacts. The system also functions tobring in an alarm, should a coin be deposited in the regular manner andan attempt be subsequently made to prevent its collection by holding thedial off-normal. In this case also relay 2I5 does not operate due to theabsence of ground and the circuit operation is blocked as hereinbeforedescribed.

The invention will now be described for its operation when the stationIOI calls an operator. As he-reinbefore stated it is a feature ofthis'invention, that no reversal of the line current is required foroperator calls, since there is no repeater equipment to be removed fromthe connection by reversal, as is the usual practice. Consequently, withthis invention, the coin-trunk circuit is not always automatically setfor collection of the coin, regardless of whether the call is to becharged for or not and is arranged so that, if the operator neglects torefund the coin by operating the coin control key, the coin isautomatically refunded on disconnection.

Let it be assumed that the coin I03 has been deposited at station IOI,that the calling party has dialed the operators number, and that brushes232 of selector SI have seized terminals 233 connecting with theoperators trunk of Fig. 3. Relay 365 will now operate over the loop ofstation IOI and operate relay 326 through an obvious circuit. Relay 326in operating will ground sleeve conductor 32'! through the winding ofretardation coil 328, and thereby cause the terminals 233 to test busyto other hunting selectors. Relay 362 will also operate relay 329 whichcloses an obvious circuit through line lamp 330 and connects a source ofgrounded ringing current 333 through resistance lamp 3 H, condenser 33I,upper make contacts of relay 329 and lower break contacts of relay 332-to the ring conductor of the line, thereby transmitting a ringing signalto I the calling station IOI. When the operator responds to the lightedlamp 330 by inserting plug 334 of cord circuit 331 into answering jack335 relay 332 operates over the sleeve from battery 333, disconnects thewindings of relay 365 from the talking conductors of the trunk with itsbreak contacts and connects ground to the winding of relay 326. Relay365 releases, releasing relay 329 which disconnects ringing currentsource 333 and extinguishes lamp 330. Holding ground is maintainedthrough the winding of retardation coil 328 by the operated contacts ofrelay 326. The operator can now, if required, extend the call over line340 by inserting plug 338 into jack 339.

Cord circuit 331 is provided with a coin control key, not shown, wherebynegative or positive coin battery may be connected, respectively, forrefunding or collecting the coin I03 at station I0 I. The coin batteryis connected to both conductors of cord circuit 331. Let it be assumedthat the operator desires to refund the coin Hi3. Refunding may beaccomplished by the operation of the coin control key, not shown, to therefund position, or automatically, when the operator and subscriber haveboth disconnected, should the operator fail to operate the refund key.When the coin control key is operated for refunding, negative coinbattery is connected to the tip and ring conductors of cord circuit 331.If the receiver at station I [II is off the hook, approximately equalcurrents will flow over the tip and ring conductors of the establishedconnection to ground through the winding of coin magnet I [0 which isactuated by the negative current and returns coin I03. Polarized relay206 on account of the differential action of the equal currents throughits windings will not operate. After the established connection isreleased by the hanging up of the receiver at station 10 l, and thewithdrawal of cord circuit plug 334 from jack the system functions toconnect automatically negative coin battery 216 to the tip and ringconductors as hereinbefore described in the case of an uncompleted call,but this operation is without effect at this time as the coin hasalready been returned. If the receiver at station I05 is on theswitchhook when negative coin battery is applied. relay 2% may operateon the current through its upper winding as the coin I B3 is returned atstation llll, in response to the negative current over the tipconductor. Under this condition relay 206 operates pick-up relay 212, asbefore described. Relay 2|2 locks to ground on break contact 225 ofrelay M3 and removes the shunt around the winding of relay 2H which,however, does not operate as the ring conductor at station Elli is nowopen. Ground on the back contacts of relay 2H now operates relay 231through the operated outer make contacts of relay 212. Relay 2Mdisconnects interrupter lead 22?, preventing the operation of relay 2l3.When the operator disconnects the selector SI releases removing groundfrom sleeve conductor 2B8 releasing relay 264. The release of relay 204causes the coin-trunk to function as hereinbefore described inconnection with an uncompleted call, negative coin battery beingconnected to the tip and ring conductors. Since the coin has alreadybeen refunded, this action is without effect at this time.

If the operator should fail to operate the coin control key, the coin isreturned automatically as before stated, as soon as the connection isreleased following disconnection of both the calling station and theoperators trunk. Under this condition the system functions as in thecase of an uncompleted call, polarized relay 265 not operating sincethere is no reversal of the battery polarity in the operators trunk.

When the operator applies positive coin battery for collecting the coinI03 none of the relays of the coin trunk of Fig. 2 operate in responsesince polarized relay 206 does not operate under this condition. Withthe receiver on the hook at station I01, positive coin current passesthrough the upper winding of relay 2% without effect; with the receiveroff the hook equal positive coin currents pass through both windings ofrelay 2% and are now without effect due to the differential action ofthe two windings. All apparatus is released following disconnection atboth calling and called ends, as before described.

What is claimed is:

1. In a telephone system, a telephone line having a pay station thereon,automatic switches for extending said line, switch-hook contacts and animpulse dial at said pay station, automatic switches'responsive toimpulses sent by said dial, means responsive to the deposit of a coinatsaid pay station for establishing a ground connection thereat to bothtalking conductors of said line, the ground connection to one of saidtalking conductors depending on said switch-hook contacts, andoff-normal contacts for said dial for removing said ground connectionfrom both sides of the line.

2. In a telephone system, a telephone line having a station with coinreceiving means thereat, means responsive to the deposit of a coin insaid receiving means for closing a ground connection to said line atsaid station, a circuit for applying current to the line to dispose of adeposited coin, means in said circuit for testing the presence of saidground connection, means effective following the application of saidcoin-disposal current for again testing said line to determine if theground connection is still present, and further test means for testingsaid line to determine the character of the ground connection at saidstation.

3. In a telephone system, a line having a station with coin receivingmeans thereat, means responsive to the deposit of a coin for closing aground connection to said line at said station, a circuit for applyingcurrent to the line to dispose of a deposited coin, relay means in saidcircuit for testing for the presence of said ground connection, meanseffective if the first test discloses a ground connection for againtesting said line to determine if such connection is still presentfollowing the removal of said coin-disposal current, and further testmeans for testing said line to determine the character of the groundconnection at said station.

4. In a telephone system, a line having a pay station thereon, meansresponsive to the deposit of a coin at said station for establishing aground connection to the conductors of said line, a source ofcoin-disposal current and means for applying it to said line, means fortesting said line to der termine whether the ground connection is stillpresent following the application of said disposal current, and othertest means effective if the first test discloses the ground connectionpresent for testing said line to determine the character of;

such ground connection.

5. The combination in a telephone system of a line having a pay stationthereon, means responsive to the deposit of a coin at said station forestablishing a ground connection to the cong' ductors of said line, acircuit for applying coindisposal current to said line to dispose of adeposited coin and open the ground connection, test means for making atest of the line after the application of said coin-disposal current todetermine whether the ground connection is still present, and furthertest means effective according to the result of said first test todetermine the nature of the ground connection.

6. In a telephone system, a line having a pay station thereon, a magnetat the pay station for disposing of a deposited coin, means responsiveto the deposit of a coin for establishing a connection from groundthrough the winding of said magnet to said line, means for applyingcurrent to the line to operate said magnet to dispose of the coin and toopen said ground connection, testing means for testing the line todetermine whether the ground connection is still present, and other testmeans for testing said line to determine the resistance of the groundconnection.

'I. In a telephone system, a telephone line having a coin stationthereon, automatic switches for extending said line to establish atalking circuit therefor, a line relay associated with one of saidswitches and connected to one of the conductors of the establishedtalking circuit, means controlled by a deposited coin for establishing aground connection to said line at said station, a circuit including saidground connection for holding said line relay energized following thereplacement of the receiver at said station, means in the establishedtalking circuit responsive to the replacement of said receiver foropening the circuit of said relay to permit the same to release, andmeans responsive to the release of said relay for causing the release ofsaid automatic switches.

8. In a telephone system, a calling line having a pay station thereon, acalled subscribers line, a series of selective switches, means foroperating said switches to establish a talking circuit from said callingline to said called line, a line relay associated with one of saidswitches, a source of current connected through the winding of saidrelay to one of the conductors of said extended talking circuit, meansresponsive to the answer by the called subscriber for reversing theconductors of said talking circuit, means responsive to the deposit of acoin at said pay station for applying a ground connection to one of theconductors of said line, a circuit including one of the talkingconductors of the established connection and the ground connection atsaid pay station for holding said relay energized following thereplacement of the receiver at said pay station, a relay in one of thetalking conductors of the established connection which releases when thereceiver is replaced at the calling station, means controlled by saidlast-mentioned relay for opening the circuit of said line relay causingthe latter to release, and means controlled by the release of said linerelay for restoring said selective switches to normal.

9. In a telephone system, a telephone line having a pay station thereon,automatic switches for extending said line, an impulse dial at said paystation, automatic switches responsive to impulses sent by said dial,means responsive to the deposit of a coin at said pay station forestablishing a ground connection thereat to both talking conductors ofsaid line, and oiT-normal contacts for said dial for removing saidconnection from both sides or" the line.

HENRY HOVLAND.

